2001 4.2 - 235 45/17 vs. 245 45/17
04-03-2012, 03:03 PM
#1
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2001 4.2 - 235 45/17 vs. 245 45/17
Hey Gents…I currently have worn 255 40/17 mounted on “Fat 5” factory rims, which I believe are 8inch rims. Looking for alternative size recommendations. I can’t decide between the 235-45/17 or the 245-45/17. Anyone have experience using this as an alternative size on the A6 4.2. I’d like to go with the 245’s but concerned with the increase in overall diameter?
Thanks in advance..!
Thanks in advance..!
04-03-2012, 07:15 PM
#2
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Increase in dia. Results in slower acceleration, worse braking, speedo error. 45 series might ride a tad softer depending on load rating of the tire.
I like conti DW tires, good price for performance.
I like conti DW tires, good price for performance.
04-03-2012, 09:07 PM
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Within a week of buying my 2000 4.2 I put on a set of 245-45/17 Conti ExtremeContact DWS tires, a decision mainly based on reading opinions in this forum. I've been very pleased with the results of that decision. I think the speedo error is 0.6 percent (BFD).
Having a sport suspension, the slight softening was OK with me. After nearly 2.5 years and nearly 25K miles, I think there may be another 10K or so left on them. Obviously, I don't drive the car very hard...but a quick 2nd gear pull now and then keeps my ya-ya's grinning for a while.
I also recommend road-force balancing.
Having a sport suspension, the slight softening was OK with me. After nearly 2.5 years and nearly 25K miles, I think there may be another 10K or so left on them. Obviously, I don't drive the car very hard...but a quick 2nd gear pull now and then keeps my ya-ya's grinning for a while.
I also recommend road-force balancing.
04-03-2012, 09:28 PM
#5
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Actually, it helps correct the speedo error...
Like most, Audi's read optimistic. The larger diameter actually gets it closer to true.
Meanwhile, remember RS6's run 255/40 18, which diameter wise is similar to 255/45 17. I have run the RS6 OEM wheels with the stock 18's (Dunlop 9000's) on my 4.2, hence know of the speedo. No obvious differences in braking, handling, ride, mileage.
From 40 to 45--which I have also experimented w in 17's--little difference in ride comfort, which surprised me a bit.
No clearance issues w/ any of these on OEM wheels, and obviously it closes up some fender gap. The RS6 wheels are 8 1/2's, though at ET30 instead of ET35 on the 8" 4.2 17's, the tire edge lands just about the same relative to the fenders. Mine is non-sport as built, though I switched to S6 bars and recently finally installed the Bilstein HD's I ordered years ago. Ride height remains stock.
Meanwhile, remember RS6's run 255/40 18, which diameter wise is similar to 255/45 17. I have run the RS6 OEM wheels with the stock 18's (Dunlop 9000's) on my 4.2, hence know of the speedo. No obvious differences in braking, handling, ride, mileage.
From 40 to 45--which I have also experimented w in 17's--little difference in ride comfort, which surprised me a bit.
No clearance issues w/ any of these on OEM wheels, and obviously it closes up some fender gap. The RS6 wheels are 8 1/2's, though at ET30 instead of ET35 on the 8" 4.2 17's, the tire edge lands just about the same relative to the fenders. Mine is non-sport as built, though I switched to S6 bars and recently finally installed the Bilstein HD's I ordered years ago. Ride height remains stock.
Last edited by MP4.2+6.0; 04-03-2012 at 09:36 PM.
04-04-2012, 04:32 AM
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goodness - all that is somewhat true, but we are talking a circumference of 1.026x that of 235/45. Not terribly much. I would suspect the larger contact patch will actually improve both lateral adhesion and braking.
All will be quite small.
G
All will be quite small.
G
04-04-2012, 10:29 AM
#7
AudiWorld Super User
Why do you think a larger contact patch would result? F=P*A, i.e., assume relatively equal sidewall force, then the only thing affecting A, contact patch area, assuming the weight of the car doesn't change, is P, tire pressure. A narrower contact patch by 10mm, for sure.
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04-04-2012, 10:33 AM
#8
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Also, you/me get 2.6% speedo change vs another guy's .6%. Since the speedo already generally reads 3-4mph fast at 60mph, 2mph won't make much difference/gets you a more accurate reading.
OTOH, the 255/40R17 on my 02S6 read exact at 60mph according to my radar gun....so a couple mph there would put me over the speed limit or within range of a 12mph grace if I'm pushing 10 over....
10mm isn't much for summer, but 20mm is significantly narrower. I run 235s in the winter tire size.
OTOH, the 255/40R17 on my 02S6 read exact at 60mph according to my radar gun....so a couple mph there would put me over the speed limit or within range of a 12mph grace if I'm pushing 10 over....
10mm isn't much for summer, but 20mm is significantly narrower. I run 235s in the winter tire size.
Last edited by SloopJohnB@mac.com; 04-04-2012 at 10:36 AM.
04-04-2012, 03:37 PM
#9
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from what i have read, tires do not behave int hat manner - and a larger tire, due to physical rigidity, does in fact have a larger contact area. In fact, look at contact prints.
Why do you think we use wider tires? If not we'd all be on 110/200-17s.
The other fallacy that we can fall into is that friction = F*c(f). In its basic definition, friction has nothing to do with area. Clearly this is wrong, w/r/t cars (or we're all really suckers, including those dumb-*** F1 teams and all their Hoyt-toity PhDs). The secret is that friction is not the limiting factor in 99.9% of dry adhesion - shear is. And more rubber = less shear.
Simple physics is simplistic. Actually, i was thrilled to see these used by Prof Lewin as fun examples in 8.01 (Classical Mechanics at MIT), since i had thought about the conundrum earlier (even asked Ross Bentley about it)
G
Why do you think we use wider tires? If not we'd all be on 110/200-17s.
The other fallacy that we can fall into is that friction = F*c(f). In its basic definition, friction has nothing to do with area. Clearly this is wrong, w/r/t cars (or we're all really suckers, including those dumb-*** F1 teams and all their Hoyt-toity PhDs). The secret is that friction is not the limiting factor in 99.9% of dry adhesion - shear is. And more rubber = less shear.
Simple physics is simplistic. Actually, i was thrilled to see these used by Prof Lewin as fun examples in 8.01 (Classical Mechanics at MIT), since i had thought about the conundrum earlier (even asked Ross Bentley about it)
G
04-04-2012, 04:44 PM
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Yep, 2.6%. Sorry, gotta remember not to trust my memory...but I keep forgetting to. Lets see if I can remember how to embed a link.
http://www.miata.net/garage/tirecalc.html
http://www.miata.net/garage/tirecalc.html